Actually, this is off by default in the patch, you have to enable "maximum-paths ibgp <1-255> equal-cluster-length" to set the BGP_FLAG_IBGP_MULTIPATH_SAME_CLUSTERLEN flag.
Daniel On Wed, Nov 11, 2015 at 1:33 PM, Paul Jakma <[email protected]> wrote: > On Wed, 11 Nov 2015, Daniel Walton wrote: > > That is a much much bigger can of worms that would have to go through IETF >> which can take a really long time. >> > > We can do it for Quagga first, and it will work for Quagga with that > capability and not bring up sessions to peers without it IF the order has > been changed - which is exactly what is needed. > > No up-front IETF work needed, though it could always be brought to IDR > later. > > Donald and I were chatting about this....I think we are overcomplicating >> this knob: >> >> - We've had this behavior for 2 years and have not had any customers hit >> any issues with it >> > > You mean, you've not had customers report they've had this issue - see > below. ;) > > - On the off chance that the stars aligned and a prefix oscillated back >> and forth between A--B one could always set local-pref, origin, etc (any >> attribute that is compared earlier than cluster-list length) to >> stabilize >> that prefix. I think the odds of that happening would be slim though, >> just >> because the IGP cost to the nexthop would likely cause A to always >> choose >> the E path. >> > > The thing is, customers might not even be able to diagnose they have this > problem. They might just have flaky routing every now and then and not > really know why. > > It took a long time to diagnose MED and IGP oscillations too (AFAIK), > never mind get a grip on the root cause of it. > > So we can avoid adding a new knob and we already have a way to work-around >> this corner case scenario. >> > > We can handle this completely transparently to the end-user too, and it's > not difficult at all. Making routing simpler for operators by making BGP > just Do The Right Thing surely is the best option? :) > > I'll whip up a patch even... > > regards, > -- > Paul Jakma [email protected] @pjakma Key ID: 64A2FF6A > Fortune: > A political man can have as his aim the realization of freedom, > but he has no means to realize it other than through violence. > -- Jean Paul Sartre >
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